This section provides background information related to the present disclosure which is not necessarily prior art.
Automatic transmissions provide a plurality of forward and reverse speed or gear ratios by selectively actuating one or more clutches and/or brakes to establish a torque-transmitting drive connection between a transmission input and a transmission output for supplying motive power (i.e., drive torque) from a powertrain to a driveline in a motor vehicle. One type of brake or clutch widely used in automatic transmission is an overrunning coupling device, commonly referred to as a one-way clutch (OWC), which overruns when one of its races (in radial coupling configuration) or one of its drive plates (in axial coupling configurations) rotates in a first (i.e., freewheel) direction relative to the other race or drive plate, and engages or locks in a second (i.e., lockup) direction. Typically, a locking member, such as a strut, associated with the one-way clutch is moveable between a non-deployed position to establish a freewheeling mode and a deployed position to establish a locked mode. The strut is commonly biased toward one of its two positions. Such conventional one-way clutches provide no independent control over their modes of operation, that is to say whether they lockup or freewheel in both directions and are commonly referred to as passive one-way clutches. Thus, basic one-way clutches provide the “locked” mode in one rotary direction and the “freewheel” mode in the opposite direction based on the direction that the drive torque is being applied to the input race or drive plate.
There are however, requirements in modern automatic transmissions where a “controllable” overrunning coupling device, commonly referred to as either a selectable one-way clutch (SOWC) or an electrically-controlled one-way clutch (EOWC), can be selectively controlled to provide additional functional modes of operation. Specifically, a controllable one-way clutch may further be capable of providing a freewheel mode in both rotary directions until a command signal (i.e., from the transmission controller) causes a power-operated actuator to shift the coupling device into its lockup mode. Thus, a controllable one-way clutch may be capable of providing a drive connection between an input member and an output member in one or both rotational directions and it may also be operable to freewheel in one or both directions. It is also known in modern automatic transmissions to integrate a passive one-way clutch and a controllable one-way clutch into a combined coupling device, commonly referred to as a bi-directional clutch.
During development testing of controllable one-way clutches at least one issue was identified that needed to be addressed. Specifically, under certain operating conditions of the automatic transmission, excessive oil levels are generated in the controllable one-way clutches in the vicinity of the deployable struts which can potentially result in unintended “hydraulic deployment” of the strut. Unintended hydraulic deployment is a condition where the strut is moved from its non-deployed position to its deployed position, independent of actuation of the power-operated actuator, due to a pressure gradient acting thereon. This pressure gradient, in combination with fluid dynamics associated with fluid flow around the clutch components, results in a force vector acting on an end portion of the strut. As this hydraulic force acting on the end portion of the strut increases in magnitude, it eventually overcomes the biasing force exerted on the strut by the strut return spring, thereby resulting in unintended partial or full deployment of the strut. Such unintended hydraulic deployment may cause the strut to “ratchet” against the inner race/drive plate which results in premature fatigue failure of the strut system and/or the armature associated with the power-operated actuator. Also, the impact may cause the armature/strut configuration to be deformed so as to result in loss of the primary latching function as the strut may only have partial deployment capabilities.
Accordingly, a need exists to continue development of new and improved overrunning coupling devices that advance the art and provide enhanced functionality.